Shadow mask mounting assemblies

ABSTRACT

The apertured mask electrode of a shadow mask color cathode ray tube is mounted adjacent to a mosaic color phosphor screen by at least three supports arranged to cause the mask electrode to move towards the screen as it expands outwardly when heated by beam bombardment. Each of the supports shown as examples includes a stud on the screen support and either a leaf spring of special shape or a combination of a leaf spring and a bi-metallic element connected between the stud and the mask electrode.

United States Patent 1191 Morrell Apr. 9, 1974 [54] SHADOW MASK MOUNTING ASSEMBLIES 3,030,536 4/l962 Hackett et al. 3l3/80 3,308,327 3/l967 Shrader [76] Invent at $2 3522? 1 3,343,024 9/1967 Torrence 313/92 B [22] Filed: Dec. 26, 1967 Primary ExaminerRobert Segal Attorney, Agent, or Firm-G. H. Bruestle; L. [2l] Appl. No.. 699,755 Greenspan vRelated US. Application Data [63] Continuation of Ser. No. 472,436, .luly l6, I965, [57] ABSTRACT abandoned The apertured mask electrode of a shadow mask color cathode ray tube is mounted adjacent to a mosaic [52] US. Cl. 313/85 S, 313/92 B, 331133729824, colorvphosphor Screen by at least three Supports ranged to cause the mask electrode to move towards 2; 29/06 g i gg g the screen as it expands outwardly when heated by l 1 o earc 1 beam bombardment. Each of the supports shown as examples includes a stud on the screen support and 1 either a leaf spring of special shape or a combination [56] References cued of a leaf spring and a bi-metallic element connected UNITED STATES PATENTS between the stud and the mask electrode. 2.846.608 8/1958 Shrader 313/85 S 2.922.063 1/1960 Haas 3l3/85 s 23 Clam, 15 Drawmg figures IATENTED 9 I974 SHEET 3 BF 3 I NVENTOR. 7 A; BERT M Mame-1L B K /QMWMF Aden-f 1 SHADOW MASK MOUNTING ASSEMBLIES This application is a continuation of my application Ser. No. 472,436, filed July I6, 1965, assigned to the same assignee, now abandoned.

This invention relates to improvements in color kinescopes and other (e.g., camera, radar and stereoscopic) cathode ray (CR) tubes of the kind containing a multiapertured mask or mask electrode through which beam electrons pass in their transit to the electron-sensitive mosaic target surface of a nearby screen.

In cathode ray tubes of the subject variety, the accuracy with which the beam electrons strike the individual elemental screen areas depends, to a great degree, upon the accuracy with which the mask apertures are aligned with the elemental screen areas during operation of the tube. Thus, in the case of a 'color kinescope, should the mask expand by reason of thermal effects occasioned by the impact thereon of the electron beam, or beams, then the resulting misalignment of the mask apertures and elemental color areas may cause the beam electrons, or some of them, to impinge upon elemental color areas other than the ones upon which they wereintended to impinge.

Several methods or means have been proposed for compensating for thermal expansion of the mask by causing the mask to move (axially) toward the screen as it expands outwardly, to maintain the desired alignment of the mask apertures and elemental screen areas. My U.S. Pat. No. 2,795,7l9'proposed movably mounting the mask within the envelope by means of three carriages attached to the periphery of the mask and sliding on inclined tracks mounted on the envelope. Van l-Iekken et al., US. Pat. No. 2,795,718 proposed the use of a multiplicity of flexible hinges connecting the masking member with a supporting frame, or a pivoted bell crank having arms slidably engaging the mask. These compensating means were designed primarily for use with circular masks in round tubes of moderate size and moderate deflection angle.

Actually, the amount of misalignment (or inisregister) of the apertures due to thermal expansion of the mask is small enough in 21 inch round 70 color kinescopes, such as the RCA 21FB22-A, to be tolerated, so that no temperature compensation is presently used. However, the problem is more severe in 90 tubes such as the 19EYP22 and AP2 2A, because of the greater deflection and the rectangular shape of the tubes. In an RCA 25AP22A color kinescope, a rectangular, cold rolled steel masking member is mounted in a rectangular envelope cap by four leaf springs each welded at one end to one side of the mask frame and having a hole at its-other end detachably engaging a stud on the envelope cap (to permit removal for successive application of the three sets of different color emitting phosphor dot areas by the conventional lighthouse procedure). The amount of radial misregister of the electron. spots relative to the intended elemental color phosphor dot areas in this tube, due to thermal expansion of the mask during operation of the tube,- is between 1 and 2 mils on a circle of about 7 inch radius. It has been found that the temperature compensating means heretofore proposed have not been satisfactory in the wider angle rectangular tubes.

An object of the present invention is to provide new and improved means for compensating for thermal expansion of an apertured mask of a cathode ray tube.

Another object is to provide effective means for maintaining the apertures of a multi-apertured shadow mask in substantial alignment with the elemental color phosphor areas in a color kinescope over the normal range of operating temperature of the tube.

The foregoing and other objects of the invention are achieved, in accordance with the present invention, by mounting a mask electrode within a tube envelope and adjacent to a mosaic screen by novel supporting means. The novel supporting means includes mounting members positively connected to the envelope and the electrode and is adapted to cause the periphery of the mask to move toward the screen, as well as outwardly, in response to heat generated by electron bombardment. The means is such that the mask movement is of an amount sufficient to maintain substantial alignment of the mask apertures with the elemental screen areas during operation of the tube. Preferably, each mounting members is detachably connected to the envelope for quick removal and replacement of the mask between successive screening operations during manufacture of the tube. In the case of rectangular tubes, four temperature-compensating mask mounting means are preferably used, each located near the mid-point of each side. However, a three-point mount incorporating temperature compensation in two different directions is also disclosed.

The invention is described in greater detail in connection with the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view, taken on line ll of FIG. 2, of a rectangular, three-beam, tri-color kinescope of the shadow-mask dot-screen variety containing a curved mask mounted in accordance with one embodiment of the present invention;

FIG. 2 is a sectional view taken on the line 22 of FIG. 1;

FIG. 3 is an enlarged axial sectional view of one of the mask mounting means of FIG. 1;

FIG. 4 is a side view, partly in section, of the mounting means, taken on line 4-4 of FIG. 3;

FIG. 5 is a view, similar to FIG. 4, of a modification thereof;

FIG. 6 is a bottom view of FIG. 5;

FIG. 7 is a view, similar to FIG. 3, of another embodim n FIG. 8 is a side view, partly in section, of the mounting means of FIG. 7, taken on line 88 thereof;

FIG. 9 is a view, similar to FIG. 8, of a modification thereof;

FIG. 10 is a side view, similar to FIG. 4, of a further embodiment;

FIG. 11 is a bottom view of FIG. 10;

FIG. 12 is a side view,- similar to FIG. I I, of a modification thereof;

FIG. 13 is a view, similar to FIG. 3, of the modification of FIG. 12;

FIG. 14 is a sectional view, similar to FIG. 2, of a rectangular-color kinescope with a three-point mask mount embodying the present invention; and

FIG. 15 is a view, similar to FIG. 4, of one of the mask mounting means of FIG. 14.

In FIGS. 1 and 2 there is illustrated a shadow-mask type color kinescope comprising an evacuated glass envelope 1 having a longitudinal axis X-X which extends through the neck 3 and funnel portion 5 of the envelope. This kinescope is of the so-called masked-target dot-screen variety wherein red, blue and green phosphor dots 6 are arranged in a mosaic pattern on the rear or target surface 7 of a glass screen-plate 9a which, in the instant case, comprises the front-end or window of the tube. The target surface 7 may be of any desired shape (e.g., circular or rectangular) and curvature (e.g., spherical or cylindrical). In the drawing, the target surface 7 is shown to be in the form of a generally rectangular section of a spherical surface. The glass screen plate 9a forms the base portion of a cup-shaped envelope cap 9 having a side wall 9b which is sealed to the funnel portion 5.

The apertured mask or mask electrode 10 for the mosaic screen 6 comprises a masking member 11, which is preferably constituted of thin (say 4 to 8 mils thick) metal (e.g., copper, nickel, iron or steel) having a positive temperature coefficient of expansion, and a peripheral reinforcing portion in the form of a rigid frame 12. Cold-rolled steel is preferably used for both the member 11 and the frame 12 because of its low cost and strength properties. Alternatively, the masking member 11 may be formed of perforated glass which has been metallized to render one or both of its main surfaces conductive. The masking member 1 l is appropriately curved with a contour similar to that of the spherical target surface 7. However, the spacing between the member 11 and the target surface 7 may be less at the outer marginal portions of the screen than at the central portions thereof, as in Epstein et al., U.S. Pat. No. 3,l09,l l6, to compensate for degrouping beam errors caused by dynamic convergence. The masking member 11 and frame 12 have generally rectangular shapes similar to but somewhat smaller than the target surface. The marking member 11 is formed with a multiplicity of apertures or holes 1 1a over most ofits area. The masking member 11 is provided with an integral, axially-extending peripheral rim portion 11b which is telescoped over and welded to an axiallyextending flange 12a of the frame 12 which has an L- shaped cross-section. The thickness of the two flanges of the mask frame 12 is normally at least ten times that of the member 11, in order to provide adequate support for the latter. The means for mounting the mask in the envelope will be described hereinafter.

The beam electrons for activating the different color phosphor areas of the screen 6 are derived from a three-beam electron gun assembly 13 mounted in the neck portion 3, e.g., as in Schroeder U.S. Pat. No. 2,595,548. The horizontal and vertical scanning forces required to impart the requisite scanning movements to the three beams from gun assembly 13 are applied simultaneously be a common deflecting yoke 15 which will be understood to comprise two pairs of electromagnetic coils disposed at right angles to each other on the neck 3. The line AA in FIG. 1 indicates the plane of deflection, which is the plane in which the axis of each deflected beam, when extended rearwardly, intersects the axis of origin of that beam. The axial location of the plane of deflection changes somewhat with changes in beam deflection. The two dashdot lines B indicate the centroid of the three beams from the plane of deflection at the maximum horizontal deflection. For a 90 tube (90 diagonal), the maximum horizontal deflection angle (between lines B) is about 78, and the maximum vertical deflection angle is about 63.

Normally, the apertured mask is mounted within the envelope of the tube by at least three, and preferably four (for a rectangular tube), leaf springs welded to the mask frame (or to a hook-plate welded to the frame) and detachably mounted on the envelope by engagement of a hole in the spring with a metal stud embedded in the envelope wall. The conventional arrangement permits radial or outward movement of the mask clue to thermal expansion but otherwise holds the mask in a unique position with respect to the mosaic target surface 7. The three different sets of red, green and blue phosphor dots are formed on the screen target surface 7 by the conventional Lighthouse" method, using the detachable mask as a stencil for exposing the appropriate portions of layers of photosensitive phosphor material. This process produces a mosaic comprising triads of red, green and blue-emitting phosphor dots 6, with the centroid of each triad substantially registered with one of the mask apertures 11a. The screening pro cess, of course, does not involve appreciable heating the mask.

When the color kinescope is operated, the masking member 11 and its frame 12 expand, due to the heat produced by electron bombardment, causing color impurity in the three-color picture on the screen due to misalignment or misregister of the apertures 11a and phosphor dots 6. In order to eliminate or minimize such misregister, the mask 10 is mounted by means including leaf springs adapted to cause the mask to move toward the screen, while expanding outwardly, in response to heat generated by electron bombardment.

FIGS. 1-4 illustrate one embodiment of the invention, in which the mask frame 12 is detachably mounted on four metal studs 17, embedded or otherwise permanently attached to the inner wall of the envelope cap 9, by four unitary mounting members in the form of L-shaped leaf springs 19. Preferably, the studs 17 and springs 19 are located at or near the midpoints of the sides of the rectangular cap 9, as shown in FIG.

2. Each spring 19 comprises at least a bi-metallic base portion or short leg 19a and a resilient portion or long leg 19b. This spring 19 may be made as an L-shaped strip of sheet spring metal with a rectangular strip of a different sheet metal bonded to the short leg of the L- shaped strip to form the bi-metallic base portion 19a. Alternatively, the entire spring 19 may be made as a strip of resilient bi-metallic sheet material. The long leg 19b is bent outwardly at an acute angle to the plane of the base portion 19a along a line 190, and formed with a hole 19d, which may be non-circular as shown, to detachably engage the stud 17. An upper part of the base portion 19a of spring 19 is welded, e.g., at points 25, to the flange 12a of the frame 12, with the masking member 11 properly positioned with respect to the screen. The base portion 19a is preformed with a bend along a line 26 to provide initial clearance between the lower part of the base portion 19a (below bend line 26) and the flange 120, as shown in FIG. 3. Thus, each spring (portion) 19b is connected to the frame 12 for movement relative thereto by means of the bi-metallic element 19a, which is integrally joined to the spring 19b at line and attached to the frame at welds 25. The materials of the bi-metallic base portion 19a are chosen so that, when heated, the lower part thereof will move inwardly toward the frame 12, in' the direction of the arrow 27 in FIG. 3. Thus, the coefiicient of thermal expansion of the metal layer next to the frame must be lower than the coefficient of the other metal layer. For example, the metal layer next to the frame may be of Invar, which has nearly zero thermal coefficient, and the other layer may be of spring steel.

In the operation of the tube shown in FIGS. 1-4, as the mask heats up, due to electron bombardment, the bi-metallic portion 19a also heats up, by conduction and radiation from the masking memberll and frame 12, and the lower part thereof moves in the direction 27. Partly due to the offset nature of the leg portion 19b, this tends to cause a movement of the hole 19d, relative to the frame 12, in the direction of the arrow 29. However, since the hole 19d is fixed by stud 17 in the envelope cap 9, the end result of the movement of the bi-metallic portion 190 relative to the frame is a component of motion of the mask 10 in the opposite direction, i.e., toward the screen, as the mask expands outwardly. Preferably, the shape of the spring 19 and the thermal coefficients of the bi-metallic base portion 19a are chosen so that the resultant movement of the mask apertures 11a at the periphery of the masking member 11 over the normal operating temperature range of the tube is substantially along the maximum deflection beam path (B in FIG. 1) to minimize misalignment or misregister of the apertures with the inv tended phosphor dots.

FIGS. 5 and 6 illustrate a modification of FIGS. 1-4, wherein the twist in the leaf spring for moving the mask toward the screen is produced by the outward expansion of the mask frame 12, rather than by the heating of a bi-metallic member. The mask frame 12 is supported on envelope studs 17 by leaf springs 33 each comprising an end portion 33a welded to'frame 12, an

- end portion 33b having a hole 33c engaged with a stud FIGS. 7 to 9 show two embodiments in which at least I an elongated portion of the mounting spring extends in a plane normal to the plane, of the mask frame and passing through the longitudinal axis of the tube. In FIGS.

7 and '8, a leaf spring 41 comprises an end portion 41a welded to the frame 12, an end portion 41b havinga hole 41c engaged with an envelope stud l7, and a-connecting portion 41d extending at an acute angle to each end portion. Preferably, the angles are such that, after mounting the mask in the envelope, the connecting portion 41d is substantiallyperpendicular to the maximum deflection beam path B, as shown in FIG. 7. In operation, the springs 41 cause the periphery of the outwardly expanding frame 12 and masking member 11 to move substantially along the path B. In the modification shown in FIG. 9, the mounting spring 45 is I..-

V shaped with a long leg 45a welded to the frame 12, as

ments shown in FIGS. 7-9 have the advantage over those shown in FIGS. l-6 that the movement of the mask 10 at each mounting means during warm-up is substantially limited to a radial plane passing through the mounting stud 17 and the tube axis.

FIGS. 10 to 13 show two embodiments wherein each mounting spring is, in effect, pivoted at opposite ends to the mask 12 and envelope cap 9 and associated with separate means for causing movement of the mask toward the screen as the latter expands outwardly. In the embodiment shown in FIGS. 10 and 11, a leaf spring 51 is pivotally connected at one end 510 to the frame 12, as by a rivet 53, and has a hole 51c at the other end 51b engaging a stud 17 on the envelope cap 9. The spring 51 is initially bent, along a line 51d, an amount sufficient to maintain the hole 510 securely engaged with the stud 17. An elongated bi-metallic strip 55 is welded at one end 55a to the radial'flange 12b of frame 12 and at the other end 55b to the edge of the end 51a of spring 51. The metals of the bi-metallic strip 55 are chosen such that the end 55b when heated tends to move relative to the frame 12 in the direction of the arrow 57 in FIG. 10, thus causing movement of the mask in the opposite direction toward the screen as the mask expands. In FIGS. 12 and 13, a leaf spring 51 is pivotally connected to the frame 12 and stud 17, as in FIGS. 10 and 11. The desired movement of the mask toward the screen in response to outward expansion thereof is produced by an inclined block or wedge element 57 welded to flange 12a of frame 12. The wedge element 57 includes an inclined surface 57a which engages the upper edge of end 51b of spring 51. Surface 57ashould be substantially; parallel to the maximum deflection beam path B, so that when, the mask expands the periphery of the mask will move along that path. A leaf-type retaining spring 59, welded to the frame 12, engages the lower edge of end 51b of spring 51 to hold the spring in contact with the wedge surface 57a.

Each of the mask mounting means shown in FIGS. 1

to 13 is especially useful in symmetrical, four-point mounts in rectangular tubes or in three or more point mounts in round tubes. When the mask is mounted asymmetrically at only three points in a rectangular tube, thermal expansion of the mask results in a transverse shift as well as an outward (radial) shift of the mask apertures relative to the phosphor dots. An arrangement for compensating for both radial and transverse misregister in a three-point mount is shown in FIGS. 14 and 15. The mask 11 is mounted in the envelope cap 9 by three leaf springs 61, 62 and 63 each attached to the mask frame 12 and pivotally connected to the cap 9 as by a hole engaging a stud 17 on the cap. The spring 61 is located near the midpoint of one side of the cap, at the l2w 0"clock position, and the two springs 62 and 63 are located on the ends of the cap, about mid-way between the other side and the horizontal center line of the cap. With conventional mounting springs which permit radial movement only, as the mask 10 expands when heated it will expand much farther upwardly (12 oclock) than downwardly (6 o'- clock), as indicated by the long and short arrows 64 and 65, respectively, in FIG. 14, because of the greater fraction of the mask above the line CC through the two end mounts than below that line. In order to maintain substantial alignment of the apertures and phosphor dots during operation, it is desirable to use mounting springs at the end mounts that will compensate for both outward and transverse expansion of the mask. Any of the temperature compensating spring means shown in FIGS. 1 to 13 can be used for the spring 61 at the 12 oclock position; however, a spring such as that shown in FIGS. 7 and 8 having no substantial lateral shift is preferred. The springs 62 and 63 may be the same type of spring as that shown in FIGS. 7 and 8 but somewhat longer, welded to the frame 12 at an acute angle thereto, as shown in FIG. 15, to cause the adjacent portions of the mask and frame to move downwardly as shown (6 oclock movement), as well as toward the sreen, in response to outward expansion of the mask. Thus, the two springs 62 and 63 extend in directions that are skewed (non-parallel and nonintersecting) with respect to the longitudinal axis XX of the tube, as distinguished from the axial arrangement of the spring 41 in FIG. 7. The length of the springs 62 and 63 should be such that the component of motion of the mask towards the screen is substantially the same as that of the spring 61.

I claim:

l. A cathode ray tube comprising:

a. an evacuated envelope having a longitudinal axis;

b. a screen having an electron-sensitive mosaic target surface mounted across said axis at one end of said envelope;-

c. an electron gun assembly mounted on said axis near the other end of said envelope for generating at least one electron beam for scanning said screen;

d. a mask electrode extending across said axis between said gun and said screen and located adjacent to said screen, said mask electrode comprising a rigid frame and a masking member mounted across said frame, said masking member containing a multiplicity of apertures through which beam electrons pass along paths toward elemental areas of said screen mosaic which are aligned with said apertures along 'said paths, said mask electrode being constituted of material that expands when subjected to heat generated by electron bombardment; and

e. means, including at least three leaf springs distributed around the periphery of said envelope, means connecting each spring with said envelope and bimetallic means connecting each spring with said frame, for mounting said mask electrode in said envelope;

said leaf springs and said bi-metallic means cooperating to move said mask electrode toward said screen, as said electrode expands outwardly in response to heat generated by electron bombardment of said electrode, an amount sufficient to maintain substantially said alignment of said apertures and elemental areas during operation of said tube.

2. A cathode ray tube as in claim 1, wherein each bimetallic means comprises a bi-metallic element integrally joined to said spring and attached to said frame.

5. A cathode ray tube as in claim 1, wherein:

a. each leaf spring has one end pivotally connected to said frame and another end formed with a hole engaging a stud on said envelope; and

b. said bi-metallic means is a separate means connected between said frame and each spring for causing said movement.

6. A cathode ray tube as in claim 5, wherein said separate means comprises an elongated bi-metallic strip attached at its ends to said frame and said other end of each spring, respectively.

7. A cathode ray tube comprising:

a. an evacuated envelope;

b. a screen having an electron sensitive mosaic target surface mounted at one end of said envelope;

0. an electron gun assembly mounted near the other end of said envelope for generating at least one electron beam for scanning said screen;

d. a mask electrode between said gun and said screen and located adjacent to said screen, said mask electrode comprising a masking portion and a peripheral reinforcing portion, said masking portion containing a multiplicity of apertures through which beam electrons pass along paths toward elemental areas of said screen mosaic which are aligned with said apertures along said paths, said mask electrode being constituted of material that expands when subjected to heat generated by electron bombardment; and

at' least three mounting means, each-including a leaf spring, said springs being distributed around 7 the periphery of said mask electrode and connected between said envelope and said reinforcing portion, for mounting said mask electrode in said envelope;

f. each of said mounting means including means for moving said mask electrode toward said screen, as said mask electrode expands outwardly in response to heat generated by electron bombardment of said electrode, an amount sufficient to maintain substantially said alignment of said apertures and elemental areas during operation of said tube.

8. A cathode ray tube as in claim 7, wherein each of said mounting means comprises a unitary mounting member including a portion of bi-metallic sheet material attached to said reinforcing portion and a leaf spring portion connected to said envelope.

9. A cathode ray tube as in claim 8, wherein each mounting member is L-shaped, with said bi-metallic and leaf spring portions constituting the short and long legs, respectively, of the L, and said long leg is bent outwardly at an acute angle to the plane of said short leg.

10. A cathode ray tube as in claim 7, wherein:

a. said envelope, screen and mask electrode have similar, generally rectangular shapes; and said mask electrode is mounted in said envelope by three of said mounting means;

1. one of said mounting means being located midversely toward said screen, in response to ther- -mal expansion of said electrode.

11. A cathode ray tube as in claim 10 wherein each of said other two mounting means comprises an elongated leaf spring extending in a direction that is skewed with respect to said longitudinal axis.

12. A rectangular shadow-mask type color kinescope comprising:

a. an evacuated envelope having a longitudinal axis and including a rectangular glass faceplate having a substantially spherical concave internal surface disposed normal to said axis;

b. a rectangular electron-sensitive mosaic three-color phosphor screen disposed on said surface;

c. an electron gun assembly mounted in said envelope and on said axis for projecting three electron beams onto said screen;

d. a rectangular domed shadow-mask electrode having a substantially spherical surface disposed adjacent to said screen in the paths of said beams, said electrode comprising a rigid metal frame and a capshaped metal masking member having an axially extending peripheral part telescoped over and welded to said frame, said masking member containing a multiplicity of apertures through which electrons of said three beams pass along paths toward elemental areas of said screen mosaic which are aligned with said apertures along said paths, said masking member and frame being constituted of a metal that expands when subjected to heat generated by electron bombardment; and

e. four mounting means, each including a leaf spring connected to said envelope and said frame and each located near the mid-point of one of the four sides of the rectangle, for mounting said mask electrode in said envelope;

f. said mounting means including means for moving said mask electrode toward said screen, as said electrode expands outwardly in response to heat generated by electron bombardment of said electrode, an amount sufficient to maintain substantially said alignment of said apertures and elemental areas during operation of said tube.

13. A cathode ray tube comprising an envelope ineluding a faceplate, a multi-apertured mask electrode comprising a peripheral reinforcing portion, and temperature compensating means mounting said electrode in said envelope in spaced relation to said faceplate; said means comprising at least three unitary mounting members distributed around the periphery of said mask electrode, each member including a bi-metallic portion attached to said reinforcing portion and an elongated leaf spring portion connected to said faceplate.

14. A cathode ray tube as in claim 13, wherein said bi-metallic and leaf spring portions of each mounting member are effectively integral.

15. A cathode ray tube as in claim 13, wherein said mask electrode comprises a multi-apertured masking member, and said reinforcing portion comprises a rigid frame attached to the periphery of said masking member.

16. A cathode ray tube comprising:

a. an evacuated envelope having a longitudinal axis;

b. a screen having an electron-sensitive mosaic target surface mounted across said axis at one end of said envelope;

c. an electron gun assembly mounted on said axis near the other end of said envelope for generating at least one electron beam for scanning said screen;

d. a mask electrode extending across said axis between said gun and said screen and located adjacent to said screen, said mask electrode containing a multiplicity of apertures through which beam electrons pass along paths toward elemental areas of said screen mosaic which are aligned with said apertures along said paths, said mask electrode comprising a peripheral reinforcing portion and being constituted of material that expands when subjected to heat generated by electron bombardment; and

e. means, including at least three bi-metallic elements distributed around the periphery of said mask electrode and each connected between said envelope and said peripheral portion, for mounting said elec trode in said envelope and for moving said mask electrode toward said screen, as said electrode expands outwardly in response to heat generated by electron bombardment of said electrode, an amount sufficient to maintain substantially said alignment of said apertures and elemental areas during operation of said tube.

17. A cathode ray tube as in claim 16, wherein the connection between each bi-metallic element and said envelope includes a leaf spring.

18. A cathode ray tube as in claim 16, wherein said mask electrode comprises a multi-apertured masking member, and said reinforcing portion comprises a rigid frame attached to the periphery of said masking member.

19. A cathode ray tube as in claim 7, wherein each of said leaf springs comprises said last-named means.

20. A cathode ray tube as in claim 19, wherein said last-named means is a bi-metallic portion of each spring.

21. In a relatively elongated color television tube having an enlarged end with mask mounting posts extending inwardly at the top and sides of said tube adjacent said enlarged end, a mask positioned in said tube adjacent said enlarged end, and spring clips connecting said posts and corresponding portions of said mask, each spring clip comprising two parts, one part being connected to its associated post and the other part being connected to the corresponding portion of said mask, and bimetal means coupling said parts for moving said mask toward said enlarged end to compensate for expansion of said mask due to temperature increase thereof.

22. The structure of claim 21 in which said bimetal means has a generally planar segment extending generally transversely of the length of said tube.

23. In a relatively elongated color television tube having an enlarged end with mask mounting posts extending inwardly at the top and sides of said tube adja- I cent said enlarged end, a mask positioned in said tube adjacent said enlarged end, and spring clips connecting said posts and corresponding portions of said mask, each spring clip being constructed and arranged for moving said mask toward said enlarged end to compensate for expansion of said mask due to temperature increase and without rotation of said spring clip about its associated post. 

1. A cathode ray tube comprising: a. an evacuated envelope having a longitudinal axis; b. a screen having an electron-sensitive mosaic target surface mounted across said axis at one end of said envelope; c. an electron gun assembly mounted on said axis near the other end of said envelope for generating at least one electron beam for scanning said screen; d. a mask electrode extending across said axis between said gun and said screen and located adjacent to said screen, said mask electrode comprising a rigid frame and a masking member mounted across said frame, said masking member containing a multiplicity of apertures through which beam electrons pass along paths toward elemental areas of said screen mosaic which are aligned with said apertures along said paths, said mask electrode being constituted of material that expands when subjected to heat generated by electron bombardment; and e. means, including at least three leaf springs distributed around the periphery of said envelope, means connecting each spring with said envelope and bi-metallic means connecting each spring with said frame, for mounting said mask electrode in said envelope; said leaf springs and said bi-metallic means cooperating to move said mask electrode toward said screen, as said electrode expands outwardly in response to heat generated by electron bombardment of said electrode, an amount sufficient to maintain substantially said alignment of said apertures and elemental areas during operation of said tube.
 2. A cathode ray tube as in claim 1, wherein each bi-metallic means comprises a bi-metallic element integrally joined to said spring and attached to said frame.
 2. the other two mounting means being respectively located along the two short sides of the rectangles and near but spaced from the other long side, and adapted to cause movement of the adjacent portions of said mask electrode laterally toward said other long side, as well as transversely toward said screen, in response to thermal expansion of said electrode.
 3. A cathode ray tube as in claim 1, wherein each bi-metallic means is a separate bi-metallic strip connected between said frame and said spring.
 4. A cathode ray tube as in claim 3, wherein each spring is pivotally connected to said envelope and said frame.
 5. A cathode ray tube as in claim 1, wherein: a. each leaf spring has one end pivotally connected to said frame and another end formed with a hole engaging a stud on said envelope; and b. said bi-metallic means is a separate means connected between said frame and each spring for causing said movement.
 6. A cathode ray tube as in claim 5, wherein said separate means comprises an elongated bi-metallic strip attached at its ends to said frame and said other end of each spring, respectively.
 7. A cathode ray tube comprising: a. an evacuated envelope; b. a screen having an electron sensitive mosaic target surface mounted at one end of said envelope; c. an electron gun assembly mounted near the other end of said envelope for generating at least one electron beam for scanning said screen; d. a mask electrode between said gun and said screen and located adjacent to said screen, said mask electrode comprising a masking portion and a peripheral reinforcing portion, said masking portion containing a multiplicity of apertures through which beam electrons pass along paths toward elemental areas of said screen mosaic which are aligned with said apertures along said paths, said mask electrode being constituted of material that expands when subjected to heat generated by electron bombardment; and e. at least three mounting means, each including a leaf spring, said springs being distributed around the periphery of said mask electrode and connected between said envelope and said reinforcing portion, for mounting said mask electrode in said envelope; f. each of said mounting means including means for moving said mask electrode toward said screen, as said mask electrode expands outwardly in response to heat generated by electron bombardment of said electrode, an amount sufficient to maintain substantially said alignment of said apertures and elemental areas during operation of said tube.
 8. A cathode ray tube as in claim 7, wherein each of said mounting means comprises a unitary mounting member including a portion of bi-metallic sheet material attached to said reinforcing portion and a leaf spring portion connected to said envelope.
 9. A cathode ray tube as in claim 8, wherein each mounting member is L-shaped, with said bi-metallic and leaf spring portions constituting the short and long legs, respectively, of the L, and said long leg is bent outwardly at an acute angle to the plane of said short leg.
 10. A cathode ray tube as in claim 7, whErein: a. said envelope, screen and mask electrode have similar, generally rectangular shapes; and said mask electrode is mounted in said envelope by three of said mounting means;
 11. A cathode ray tube as in claim 10 wherein each of said other two mounting means comprises an elongated leaf spring extending in a direction that is skewed with respect to said longitudinal axis.
 12. A rectangular shadow-mask type color kinescope comprising: a. an evacuated envelope having a longitudinal axis and including a rectangular glass faceplate having a substantially spherical concave internal surface disposed normal to said axis; b. a rectangular electron-sensitive mosaic three-color phosphor screen disposed on said surface; c. an electron gun assembly mounted in said envelope and on said axis for projecting three electron beams onto said screen; d. a rectangular domed shadow-mask electrode having a substantially spherical surface disposed adjacent to said screen in the paths of said beams, said electrode comprising a rigid metal frame and a cap-shaped metal masking member having an axially extending peripheral part telescoped over and welded to said frame, said masking member containing a multiplicity of apertures through which electrons of said three beams pass along paths toward elemental areas of said screen mosaic which are aligned with said apertures along said paths, said masking member and frame being constituted of a metal that expands when subjected to heat generated by electron bombardment; and e. four mounting means, each including a leaf spring connected to said envelope and said frame and each located near the mid-point of one of the four sides of the rectangle, for mounting said mask electrode in said envelope; f. said mounting means including means for moving said mask electrode toward said screen, as said electrode expands outwardly in response to heat generated by electron bombardment of said electrode, an amount sufficient to maintain substantially said alignment of said apertures and elemental areas during operation of said tube.
 13. A cathode ray tube comprising an envelope including a faceplate, a multi-apertured mask electrode comprising a peripheral reinforcing portion, and temperature compensating means mounting said electrode in said envelope in spaced relation to said faceplate; said means comprising at least three unitary mounting members distributed around the periphery of said mask electrode, each member including a bi-metallic portion attached to said reinforcing portion and an elongated leaf spring portion connected to said faceplate.
 14. A cathode ray tube as in claim 13, wherein said bi-metallic and leaf spring portions of each mounting member are effectively integral.
 15. A cathode ray tube as in claim 13, wherein said mask electrode comprises a multi-apertured masking member, and said reinforcing portion comprises a rigid frame attached to the periphery of said masking member.
 16. A cathode ray tube comprising: a. an evacuated envelope having a longitudinal axis; b. a screen having an electron-sensitive mosaic target surface mounted across said axis at one end of said envelope; c. an electron gun assembly mounted on said axis near the other end of said envelope for generating at least one electron beam for scanning said screen; d. a mask electrode extending across said axis between said gun and said screen and located adjacent to said screen, said mask electrode containing a multiplicity of apertures through which beam electRons pass along paths toward elemental areas of said screen mosaic which are aligned with said apertures along said paths, said mask electrode comprising a peripheral reinforcing portion and being constituted of material that expands when subjected to heat generated by electron bombardment; and e. means, including at least three bi-metallic elements distributed around the periphery of said mask electrode and each connected between said envelope and said peripheral portion, for mounting said electrode in said envelope and for moving said mask electrode toward said screen, as said electrode expands outwardly in response to heat generated by electron bombardment of said electrode, an amount sufficient to maintain substantially said alignment of said apertures and elemental areas during operation of said tube.
 17. A cathode ray tube as in claim 16, wherein the connection between each bi-metallic element and said envelope includes a leaf spring.
 18. A cathode ray tube as in claim 16, wherein said mask electrode comprises a multi-apertured masking member, and said reinforcing portion comprises a rigid frame attached to the periphery of said masking member.
 19. A cathode ray tube as in claim 7, wherein each of said leaf springs comprises said last-named means.
 20. A cathode ray tube as in claim 19, wherein said last-named means is a bi-metallic portion of each spring.
 21. In a relatively elongated color television tube having an enlarged end with mask mounting posts extending inwardly at the top and sides of said tube adjacent said enlarged end, a mask positioned in said tube adjacent said enlarged end, and spring clips connecting said posts and corresponding portions of said mask, each spring clip comprising two parts, one part being connected to its associated post and the other part being connected to the corresponding portion of said mask, and bimetal means coupling said parts for moving said mask toward said enlarged end to compensate for expansion of said mask due to temperature increase thereof.
 22. The structure of claim 21 in which said bimetal means has a generally planar segment extending generally transversely of the length of said tube.
 23. In a relatively elongated color television tube having an enlarged end with mask mounting posts extending inwardly at the top and sides of said tube adjacent said enlarged end, a mask positioned in said tube adjacent said enlarged end, and spring clips connecting said posts and corresponding portions of said mask, each spring clip being constructed and arranged for moving said mask toward said enlarged end to compensate for expansion of said mask due to temperature increase and without rotation of said spring clip about its associated post. 